A styrene polymer produced by the radical polymerization method, etc. has an atactic configuration in stereostructure. It is molded into various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding, for example, and has been widely used for electric domestic appliances, office equipments, domestic appliances, packaging containers, toys, furniture, synthetic papers and other industrial materials.
However, the styrene polymer having an atactic configuration has drawbacks that it is inferior in heat resistance and chemical resistance.
The group of the present inventors have succeeded to develop a styrene polymer having a high degree of syndiotacticity, and also developed a styrene copolymer in which other components are blended with the styrene monomer (Japanese Patent Application Laid-Open Nos. 104818/1987 and 241009/1988). Such polymer or copolymer having a syndiotactic configuration has excellent heat resistance, chemical resistance and electric characteristic, and expected to be applied in various fields.
However, the above polymer, particularly, syndiotactic polystyrene is a polymer wherein glass transition temperature is 90.degree. to 100.degree. C. and melting point is 250.degree. to 275.degree. C. Heat deformation temperature under light load is high level, i.e. around melting point, while heat deformation temperature under heavy load is around glass transition temperature, that is, it is almost the same as that of general-purpose polystyrene (GPPS).
For improvement of the properties of styrene polymer having syndiotactic configuration, we proposed to compound it with other thermoplastic resin, inorganic filler and the like. But there are still some room for improvement in adhesion of the interface and compatibility.
Accordingly, the present inventors have studied intensively to develop a copolymer whose impact resistance is improved while maintaining heat resistance and chemical resistance of a polystyrene having a syndiotactic configuration, or a copolymer whose heat resistance is further improved by raising glass transition temperature (heat deforemation temperature under heavy load) or heat decomposition temperature, which has good compatibility and adhesion to other resin or inorganic filler and improved wettability, and further to develop an efficient process for production of said copolymer.
As the results, we have found that copolymerization of a styrene monomer with (1) an acrylonitrile monomer, (2) an unsaturated carboxylic acid or its ester monomer or (3) a maleimide or N-substituted maleimide monomer in the presence of a specific catalyst provides a copolymer having a configuration wherein the above monomer (1), (2) or (3) is copolymerized onto the styrene repeating unit chain having a syndiotactic configuration, said copolymer being excellent in heat resistance, chemical resistance, impact resistance or the like, having high heat deformation temperature under heavy load and presenting good wettability whereby the objective improvement can be achieved. The present invention has been accomplished based on such findings.